The invention relates generally to the field of communication systems and more particularly to multiplex layer functionalities for multiplexing/demultiplexing data between Link Layer Protocol instances and physical channels of the transport layer.
In third-generation CDMA systems, the services supported consist of a variety of data rates and delay profiles. Therefore, the rate of data flow from the upper protocol layers to the link layer varies in real time for a particular service and also among services. As a result, the number and sizes of link layer Protocol Data Units (PDU""s) provided to the physical layer and their associated sizes varies from one physical layer frame duration to another. For the case of cdma2000, for example, the frame duration is fixed at 20 ms.
An attempt to improve error detection with such an array of data possibilities has involved a multiplexing scheme with repetition of link layer data blocks to achieve a fixed size logical transmission unit (LTU), with a Cyclic Redundancy Check (CRC) then being added to each LTU. However, performing repetition after adding the CRC (i.e., associating a CRC with each link layer data block multiplexed into the LTU) would improve the error detection and correction at the receiving end, since there would then be a plurality of copies each with its own CRC, thus improving the odds receiving one in which the CRC checks out correctly.
Accordingly there exists a need for a system and method of adding improving error detection and correction by adding CRC to variable size link layer data blocks before performing repetition to achieve a fixed-size LTU.
Accordingly it is an object of the present invention to provide systems and methods of adding improving error detection and correction by adding CRC to variable size link layer data blocks before performing repetition to achieve a fixed size LTU.
It is another object of the present invention to provide such a system and method which includes repetition by mapping different numbers of LTU""s to a fixed size physical layer frame.
These and other objects of the invention will become apparent to those skilled in the art from the following description thereof.
In accordance with the teachings of the present invention, these and other objects may be accomplished by the present multiplex layer mapping of Link Layer PDU""s to frames of the Physical Layer.
An embodiment of the invention includes a method of multiplexing Radio-Link Protocol (RLP) PDU""s onto physical-layer frames including aggregating at least one RLP PDU into a first block; adding error detection and/or correction encoding (such as a cyclic redundancy check (CRC)) to the first block, mapping as many copies of the first block as possible into an fixed-size second block, and mapping as many copies of the second block as possible into a physical-layer frame.
The present invention proposes a solution for the multiplex layer to multiplex/demultiplex RLP PDU""s to/from physical frames. Error detection and/or correction is improved by including CRC information prior to any repetitions of PDU""s when mapping to the physical-layer frame. Repetition and zero bits padding may be applied at both the second-block level and the physical-layer frame level. Then the PDU recovery process at the receiving station may be performed in 2 stages: recovery of the second block from the physical-layer frame, and recovery the PDU""s from the second block. The multiplicity of copies, each with its own CRC, enhances the probability of successful recovery of each PDU.
The invention will next be described in connection with certain exemplary embodiments; however, it should be clear to those skilled in the art that various modifications, additions and subtractions can be made without departing from the spirit or scope of the claims.